(1) The Field of the Invention
The present invention relates to a photocopying apparatus and particularly to a photocopying apparatus, which is capable of performing real size, reduction and enlargement photocopying by using a zoom lens.
(2) Description of Prior Art
As photocopying apparatus, there exists a magnification changing photocopying apparatus, which has the ability to perform enlargement and reduction reproduction as well as real size reproduction. A magnification ratio changing device which performs a reduction reproduction at the rate of 0.866 and 0.707 and also produces enlargement reproduction at the rate of 1.155 and 1.414 is already known. At present, a zoom lens is commonly used in an optical system.
FIG. 1 shows a a prior art photocopying apparatus and FIG. 2 is a diagram illustrating the relationship between the mirror moving area and the lens moving area in FIG. 1.
In FIG. 1, a contact glass 2 which is used as a plate (the original placing plate) on which the original is placed is located on the upper part of the photocopying apparatus body 1. A reflecting plate 4 is provided at the rear of an exposing lamp 3 which is composed of fluorescent light together with other components. The illumination of the original from the exposing lamp 3 occurs without loss. The reflected light from the original is incident on the first mirror 5.
The illumination device 6 is chiefly composed of the above-mentioned exposing lamp 3, reflecting plate 4, the first mirror 5. The illumination device 6, which performs the reciprocal scanning from one end to the other end of the original, which is placed on the contact glass 2, thereby illuminating the original by light from the exposing lamp.
The light reflected from the original is incident to the first mirror 5 in the illumination device 6. The light reflected by the first mirror 5 is further reflected by the second mirror 7 of the mirror unit 9 which is composed of the second mirror 7 and the third mirror 8, thereby entering into a zoom lens 10 through the third mirror 8.
The light passing through the zoom lens 10 is reflected by the fixed mirror 11 and is projected onto the photosensitive surface 12a of the photosensitive drum 12, thereby forming an electrostatic latent image of the original onto the photosensitive surface 12a.
The electrostatic latent image on a photosensitive surface 12a is developed by a developing device 13, thereby forming a visible image of toner. This toner image on the photosensitive surface 12a is transferred onto the copying paper 15 which is fed by the paper-feeding device 14 by an image-transferring device 16. The paper transporting device 17 then transmits the paper to a fixing device 18 to perform a heat fixing operation, and then the paper is ejected onto the tray 19.
On the other hand, the photosensitive surface 12a having passed through the image-transferring device 16 is subject to a discharging process by a discharge device 20. Then the toner remaining on the photosensitive surface 12a without being transferred to the copy paper is cleaned by a cleaning device 21. A device 22 establishes a uniform charge on the photosensitive surface 12a which waits for an exposure to be conducted by the fixed mirror 11. The copying operation is performed on the copying paper 15 by repeating these processes. The heat produced during the copying process is exhausted outside the apparatus by the blower 23 located within the apparatus.
When the copying cycle is performed the illumination device 6 is scanned at a constant speed towards the right direction and the exposure lamp 3 illuminates the original from one end thereof to the other. Then, simultaneously, the mirror unit 9 is moved towards the right direction at half the scanning speed, so that the length of the light path from the position of the illuminated original to the position of the zoom lens 10 is not varied.
When the magnification ratio is changed, the zoom lens 10 is moved from the reference position (shown by a solid line) to the position shown by a dotted line. For example, when an enlargement is conducted, the position of the zoom lens 10 is moved to position 10a. When a reduction is conducted, the position of the zoom lens is moved to the position 10b.
FIG. 2 shows a positional relationship between the mirror unit 9 and zoom lens 10 at the time of enlargement, real size and reduction reproduction. During real size reproduction, mirror unit 9 located at the start position of the scanning operation, namely, the home position, designated by a solid line, moves to the end position 9a of the scanning operation for a distance of L.sub.1. Even if the mirror unit 9 is moved until the end 9a position of the scanning, the mirror unit 9 is separated from the zoom lens 10 by the distance D.sub.1.
During enlargement, the zoom lens 10 is moved from the real size reproduction position towards the left by the distance L.sub.4 from the position for the real size reproduction. In this instance, as the size of the maximum original which can be copied onto the copying paper of the predetermined size is smaller in comparison to the real size reproduction, the scanning distance of the illumination device 6 can be made shorter than the scanning distance at the time of the real size reproduction. Accordingly, the moving distance L.sub.2 of the mirror unit 9 is also made shorter than the moving distance L.sub.1 at the real size reproduction (as shown in FIG. 2).
When a reduction reproduction is performed, the zoom lens 10 is moved from the real size reproduction position towards the right direction by the distance L.sub.3. In this case, the scanning distance of the mirror unit 9, which is moved at the time of copying the original is the same as that of real size reproduction, that is, L.sub.1. As is clear from the above description, the position 10a of the zoom lens 10 at the time of enlargement reproduction is included in the scanning area (distance L.sub.1) of the mirror unit 9 at the time of reduction reproduction. This means that, if the mirror unit 9 scans along the scanning distance L.sub.1 as if real size or reduction reproduction had occurred, such that the zoom lens 10 is located at the position 10a for the enlargement reproduction, the mirror unit 9 would collide with the zoom lens 10. To prevent this problem, the scanning distance of the mirror unit 9 must be limited so that the mirror unit 9 does not invade the moving area of the zoom lens. To accomplish this countermeasure in prior art devices, the first limit switch 25, which limits the scanning distance of mirror unit 9 in case of real size or reduction reproduction, and the second limit switch 26, which limits the scanning distance of mirror unit 9 in case of enlargement reproduction, are individually disposed. (The second limit switch 26 is located before the first limit switch 25 in the scanning path of the illumination device 6 and both of them are actuated by the illumination device 6 which scans in connection with the mirror unit 9.)
However, even if the above-mentioned over-scanning countermeasure is employed, the mirror unit 9 may stop at a intermediate position between the first limit switch 25 and the second limit switch 26. In other words, the mirror unit 9 may pass through the position 9b and may stop in the vicinity of the position 9a because of a paper jam or any other accident which occurs during the process of real size or reduction reproduction.
Under these circumstances, when the enlargement reproduction operation is performed, the zoom lens 10 is moved to the position 10a and collides with the mirror 9. Such a state is sometimes caused when the electric power is turned off during the copying cycle. In order to avoid such an unexpected situation, the distance between the mirror unit 9 and zoom lens 10 can be designed larger so that the mirror unit 9 does not collide with the zoom lens 10 when the zoom lens 10 reaches the position 10a for an enlargement reproduction. However, if the distance is extended, the focal length f of the zoom lens 10 is also extended. While the equation F=f/D is established where the diameter of the lens is D, the brightness of the lens is F. As is clear from this equation, when the focal length is extended with regard to the same diameter of the lens, the brightness of the lens is lowered. It is therefore necessary to increase the quantitity of light from the exposing lamp 3 or to increase the diameter of the zoom lens 10 for the purpose of obtaining the same quantity of light on the photosensitive surface 12a. However, when the quantity of the light from the exposing lamp 3 is increased, the temperature adjacent to the exposing lamp 3 is increased and when the diameter of the zoom lens 10 is increased, the cost goes up, which means that the apparatus as a whole is not assembled in a compact manner.